Tissue coagulation apparatus and method

ABSTRACT

A device and system for the cutting and/or coagulation of human tissue with the use of high frequency currents. This invention is used to cut materials similar to the human tissue which can emit steam or gassy products when sufficiently heated. It controls the extent of the arc generated during the cutting operation, and controls the heat generated during the coagulating operation, both of these for the purpose of minimizing formation of harmful forms of albumen.

CROSS-REFERENCE TO CO-PENDING APPLICATION

This is a division of applicants' co-pending application Ser. No.709,610, filed July 29, 1976, entitled Cutting and Coagulation Apparatusfor Surgery, now U.S. Pat. No. 4,114,623.

This invention relates to a device for the cutting and/or coagulation ofhuman tissue with the use of high frequency currents. This invention isgenerally useful for the surgical cutting of materials that are similarto human tissue; that is, such materials as will emit steam or gassyproducts when sufficiently heated, and which have enough conductivity ordielectric losses that they will be heated by high frequency currents.

It is a well-established procedure to cut human tissue with the use of aprobe in the form of a thin wire or a thin knife, using a high frequencyalternating electrical current applied to the tissue by the probe actingas one electrode. The other electrode is attached elsewhere to the body.The thin probe has a small cross-section where it touches the area ofthe body to be cut, and therefore there is a very high current densityat this place. The term "probe" includes a knife, a thin wire, or anyother suitably thin current-applying body. Because of the relativelylarge resistance loss in the human tissue with the use of high frequencycurrents, there occurs a heating of the tissue, especially in view ofthe high current density at the small-area point of contact of the probewith the tissue. Because the tissue contains water or fat (substancesthat will steam away), the alternating current creates a steaming off offluid in the tissue, thereby destroying the cell walls. This will occurat higher temperatures in the proximal areas of the point of contact ofthe probe and will cause a division of the tissue at this region.Pushing the probe along will cause a continuous cut to be made in thismanner.

It is well known that, by means of the aforementioned procedure, abloodless cut can be made. This derives from the fact that heating ofthe cut tissue causes a boiling of the albumen and sealing of thecapillaries. If larger blood vessels are cut, the usual procedure forsealing the vessel is to halt the probe for a time at the respectivearea in order to provide a greater amount of heat, and spread this heatto and through the tissue, the wall of the artery, and the blood, forthe purpose of causing coagulation.

At the moment when the steaming away of water or fat occurs, theimmediate region of contact between the probe and the tissue changesinto a gaseous separation layer. The high frequency current flowsthrough this gaseous separation layer with the help of an electric arcthat itself produces a very high temperature. This high temperature maylead to the destruction of albumen to a larger extent than is desirable,and especially may lead to the production of poisonous forms of albumen.The poisonous forms of albumen will seriously hinder the healing processwhich follows the surgery and are therefore undesirable. Furthermore,the electric arc produces a mixture of gaseous oxygen and hydrogen fromthe water. The high frequency current used for cutting the tissue hasbeen known to cause dangerous oxygen-hydrogen explosions. Accordingly,it is desirable to control the existence and effects of the electricarc.

The adjustment of the high frequency current to the correct intensity iscritical since, on the one hand, cutting will only occur as theconsequence of formation of gases, but on the other hand, an excessiveelectric arc has to be avoided because of the damage it might do, forexample, excessive formation of deleterious forms of albumen. However,for the rapid sealing of the larger vessels, sufficient heat should bemade available, but without the presence of an electric arc.

To complicate matters further, human tissue is not homogenous, and anincision may progress through zones of different types of tissue, forexample, through regions of greater water density, through scar tissueof little water density, through fat, and through skin. So theelectrical resistance of the tissue will usually vary with the progressof the incision, as will the current passed through the circuit, and theformation of gases. For this reason, if an unregulated generator isused, sometimes too much gas formation and too strong an electric arcwill occur, while at other times not enough heat will be available andthe cutting process will stop. Therefore, during the cutting process,the magnitude of the high frequency current should be kept adjusted soas to conform to the needs of the tissue being cut at the moment.Experience shows that the usual adjustment of the current by the surgeonwhen using presently-known devices is hardly optimal.

It is an objective of this invention to regulate the magnitude of thehigh frequency current supplied to the probe, by means of an automaticcontrol unit with a sufficiently rapid response that the currentsupplied at least closely conforms to the required optimal current forthe tissue then being cut. This means there should always be enoughcurrent for the cutting and coagulation process, but on the other hand,only such an amount as limits the formation of electric arcs to thecorrect extent.

This objective finds its solution in this invention by utilizingindicating means which supplies information, continuously or atpredetermined intervals, about the on-going cutting and coagulationprocesses in the form of one or more electrical signals. There may alsobe provided a control means which compares the output of the indicatingmeans to a set-point program, to produce a control voltage from thecomparison. With the use of this control voltage, the output current ofa high frequency generator that supplies current to the probe isadjusted to values prescribed by the set-points and suitable to theneeds of the procedure at the moment.

The indicating means can be of various known types. For example, theelectric arc can be sensed by optical means, and the electrical signalcan be derived therefrom by the use of an optical-electrical transducerresponsive to the optical means. However, all-electrical measuringmethods seem to be preferable. For example, those that observe theelectrical resistance of the high frequency current, or that willobserve delivered power of the high frequency current to the coagulatingprocess, are useful.

This invention will be fully understood from the following detaileddescription and the accompanying drawings, in which:

FIG. 1 is a schematic circuit drawing showing circuitry according to theprior art;

FIG. 2 is a schematic circuit drawing showing a simple embodiment of theinvention;

FIGS. 3 and 4 are schematic circuit drawings showing twomore-sophisticated embodiments of the invention; and

FIG. 5 is a graph showing a mode of operation of one of the embodimentsof the invention.

FIG. 1 shows the conventional high frequency tissue cutting device. Itincludes a high frequency generator 1 which produces voltage and currentat high frequencies to leads 2 and 3. Lead 2 is connected to conductiveprobe 4 having a fine edge which will make a small-area contact withtissue 6. Probe 4 is one electrode for the system. The other electrode 5is applied to the tissue by means of a firm wide area abutment contact.The circuit is completed through tissue 6.

Throughout the specification identical numbers are applied to identicalmeans.

FIG. 2 shows a simple example of apparatus which will observe thecutting and/or coagulation states directly through leads 2 and 3.Indicating means 7 is connected into leads 2 and 3. The output of theindicating means is provided by means of an electrical signal to controlmeans 8 through 11. This control means also receives data from aset-point program contained in a reference setter 9. Through leads 10,the magnitude of the high frequency current produced by the generator 1is controlled as a consequence of the signal from means 8. The set-pointprogram is selected prior to the operation by the surgeon in accordancewith the procedure to be undertaken and will be more fully describedbelow. Suffice it to say that the purpose of the control means is todetermine the magnitude of the curr produced by the generator, which ofcourse has a substantial effect upon the existence and volume of an arcand the amount of heat generated.

The indicating means can respond to one or more physical values. Theindicating means must measure and show the presence and strength of theelectric arc, because the limitation of the volume of the electric arcto special safe values is a feature of this invention and secures anoptimal medical result. On the other hand, cutting with a useful cuttingspeed will produce substantial amounts of gases, and the existence of aminor electric arc is inevitable. With low current magnitudes, noelectric arc will start. The high frequency voltage between probe andtissue is then insufficient, and cutting does not occur. With anincrease in the magnitude of the high frequency current, the electricalarc starts suddenly, when at higher currents the output voltage of thehigh frequency generator exceeds the ignition voltage of the electricarc. This is called the ignition point of the electric arc. The ignitionpoint depends importantly on the characteristics of the tissue at thepoint of contact with the probe. The ignition point may be exceeded onlyslightly, if burning of albumen is to be avoided or minimized.

This invention always refers the set-point to the ignition point of theelectric arc. By way of example, during a constant speed of incision,and without need for pausing for coagulation, the set-point program ofthe device will be arranged to control the output power of the highfrequency generator in such a way that the ignition point is exceededonly slightly, and therefore a minor electric arc exists. This is alsotrue for heterogenous tissue, because the output power of the highfrequency generator will permanently be referred to the ignition pointas it exists from point to point along the cutting path. In the eventthe coagulation procedures become necessary, use is made of acoagulation set-point which causes temporary changes of the currentmagnitude. The maximum value of the magnitude of the high frequencycurrent is related to the ignition point of the electric arc, but arcignition is not permitted to occur for substantial periods of timeduring coagulation.

From the foregoing it follows that a very precise indicating procedurefor the ignition point and the strength of the electric arc is needed ifthe incision and coagulation procedures are to work at an optimum level.An advantageous indicating means 7 for a very accurate measurement ofthe ignition point, and the strength of the electric arc, will now bedescribed. The alternating voltage produced by the generator 1 drivesthe current from the probe 4 into the tissue 6. At times when theinstantaneous value of the high frequency voltage is small, no electricarc will exist. An electric arc will appear as the voltage increases(provided the maximum value is sufficiently high). When the voltagedecreases after passing its maximum, the electric arc disappears again.Therefore, the electric arc burns, if it burns at all, only during apart of the period of the current alternation. During this time, itchanges the resistance of the circuit, and influences the correspondingcharacteristics of the current. It is therefore possible to measure theelectric arc either from the changing circuit resistance, or from thechanging current, or from the changing voltage, all caused by theelectric arc.

A preferred technique to make the necessary measurement is to employ thechange in the current through the electric arc. As soon as the electricarc burns, the sinusoidal current delivered from the high frequencygenerator will be distorted by the additional "harmonic" components ofthe current generated from the electric arc itself. Since the distortionin the positive and the negative half-periods of the current are aboutequal, the distortion appears almost only as harmonic frequencies whichare odd numbered (preferably tripled) relative to the working frequencyfrom generator 1. The extent of the distortion increases with theincreasing size (volume) of the electric arc. The measurement of theharmonic distortion contained within the high frequency alternatingcurrent provides an indication of the volume of the electric arc, and iswell suited for control purposes in this invention.

Because the cutting procedure must work with a very small electric arc,it is important to be able to make measurements of very small harmoniccurrent components from the arc itself. A small electric arc producesonly a small amount of harmonic distortion which is of the same order ofmagnitude as would, without precautions, be delivered by a conventionalgenerator 1. Therefore, a filter 12 (FIG. 3) is an important component.This filter is designed in such a way that it will pass the current ofthe working (base) frequency from the generator almost withoutattenuation. However, it attenuates and filters out currents of harmonicfrequencies almost completely, and therefore prevents the power supplyfrom delivering its usually-existing harmonic current components to theprobe. Then the electric arc between probe 4 and tissues 6 issubstantially the only source of harmonic current components.Measurement of these harmonics thereby provides an indication of thevolume and intensity of the electric arc.

Because relatively large currents at the working frequency flow fromfilter 12 to probe 4 and electrode 5, in addition to the harmoniccurrent components of the electric arc which are to be measured, anotherfilter 15 is preferably, but not necessarily, inserted into the circuit(FIG. 3). It isolates measuring means 16 from the currents of workingfrequency, and passes to measuring means 16 only the harmonic currentcomponents which are to be measured.

The harmonic current components passed by filter 15 can be measured byknown high frequency ammeters as one example of measuring means 16. Whenusing a measuring means of this type, it is an advantage to design thecouplings 13, 14 of the circuit to filter 12 with a very low impedancefor the harmonic frequencies. Then the circuit has the lowest possibleresistance to the harmonic current components, and the electric arc willproduce the largest possible harmonic components. Thus, the output ofthe harmonics used to provide measurement is optimized.

Using modern instrumentation, it is somewhat easier to utilize theinertia-free techniques attainable with voltage measurements thanindication means relying on current flow which involve elements that dopossess inertia. Therefore, filter 12, in the presently preferredembodiment and best known mode for the invention, as shown in FIG. 4, isdesigned in such a way that the couplings 13, 14 possess a highimpedance for the harmonic frequencies that are to be measured, and theyare directed toward these couplings. Then the harmonic currentcomponents between couplings 13 and 14 produced by the electric arccause correspondingly high harmonic voltage components. In FIG. 4 thesecomponents pass through filter 17 that passes them to a high frequencyvoltage meter 18. This is an inertia-free device. Filter 17 filters outthe voltages of the basic frequency from the generator, and preventstheir reaching the measuring means 18.

If the frequency of the generator is exactly defined and stable, thenfilter 15 (in FIG. 3) or filter 17 (in FIG. 4) can have a smallband-pass, and allow essentially only one harmonic frequency (preferablythe third) to pass through. If the frequency of generator 1 is notprecisely defined and stable, then filters with larger band widths willbe used.

In the preferred embodiment of the invention, one would use a filterwith a high pass character that allows passage of all the harmoniccomponents from the arc. This way the voltage of the harmonics to bemeasured will be larger and easier to measure through summing up.However, the selection of the working frequency (i.e., the frequency ofthe generator) may be worse than with the narrow band filter.

In order to be able to measure the ignition point of the electric arccertainly and exactly, one uses a voltage measuring device that will besensitive enough to measure even very small voltages. In a preferredembodiment of this invention, the voltage measuring means may comprise alinear diode rectifier with a pre-amplifier. The band width of thepreamplifier is adjusted to the frequency band of the anticipatedharmonic components which are to be measured. In one beneficialarrangement, the set-point program can be adjusted by the surgeon. Thisregulation, in its simplest form, occurs in such a way that the signalvoltage fed through line 11 (FIG. 4) is maintained at a constant levelby means of the control device. Such an arrangement enables cutting witha substantially constant cutting speed, nearly independently of thetissue composition at the moment, because the high frequency current isalways regulated so that a minor electric arc burns to a nearly constantextent. As long as no fairly large blood vessels have to be cut, theheating of the tissue through this "set-point" voltage program can beadjusted automatically. Then coagulation and blood volume of the tissuecan be taken into account during cutting.

If the tissue has a tendency to bleed, and if not enough coagulationresults along with the normal cutting process, then the set-pointprogram will be shaped in such a way that cutting intervals andcoagulating intervals will alternate, with adjustable respective pulsedurations. During the cutting intervals, the control will follow theset-points of the electric arc as mentioned above. During thecoagulation intervals, the magnitude of the high frequency current willbe reduced from the higher values where an arc exists and cuts, to alower level where the arc does not exist, and therefore cutting does notoccur. During the coagulation intervals, the probe will be heldmotionless in the same place with respect to the tissue, with heatingcurrent applied at levels below those which cause an arc. This effectwill heat the tissue in the contacted area to the higher temperatureswhich are needed so that coagulation can occur, but not to the highertemperatures which would cause steaming off and cutting.

The effect of the high frequency current depends on how much themagnitude of the current fluctuates at or below the level at which thearc will start. If a surgeon should cut an area of tissue with differentcharacteristics from other tissue, the current magnitude has to changeaccordingly, because the ignition point of the electric arc alsofluctuates. Therefore, the demand for current for the cutting and forthe coagulation processes vary. In an advantageous form of thisinvention, the current magnitude of the set-point program will not begiven as a constant value for all conditions and tissues, but instead isgiven as a relative value, relative to the reignition point of theelectric arc in the tissue where the probe is working.

There are differences in the set-point values in the cutting intervaland in the coagulation interval. In the cutting interval, a small arcshould always be burning so that the indicating device always produces asignal, with the help of which the set-point program can be utilized tocontinue the cutting action. In the coagulation interval, there shouldbe no burning electric arc. Therefore, there is no signal given by theindicating device to give any reference or setting, and no signal willbe given by the indicating device. If the characteristics of the tissueshould change, for example through warming up by means of thecoagulation process, or through changes in the line voltage of thegenerator, then there would be no criteria in the indicating meansrelating to the ignition point of the electric arc as long as theelectric arc is not burning.

In an advantageous form of this invention, the set-point program isarranged in such a way that, during the coagulation process, the currentwill be increased periodically in short bursts to locate the ignitionpoint of the electric arc. FIG. 5 shows a typical time sequence for themagnitude of the high frequency current for this purpose. This is theordinate of the graph. The abscissa is time. The interrupted line showsa typical time dependence of the ignition point of the electric arc in atissue of varying composition. This broken line shows the current levelat and above which an arc will burn, assuming proper voltage. The curvesare not horizontal, because it is assumed that the composition of thetissue is changing. The solid line curve shows the real course ofcurrent magnitude (I) that is controlled by the set-point program. Itshows at segments "a" the current in time intervals in which the cuttingprocess occurs. At this time, the current lies above the ignition pointof the electric arc and an arc burns. Segments "b" are the timeintervals during the coagulation process. In these intervals, thecurrent will drop below the ignition point of the electric arc and noarc burns, but current is passed to create heat. However, during thesesegments, there is no signal from the measuring means. To overcome thisdeficiency, points "c" show moments in time in which the currentmagnitude (only during coagulation procedure) is periodically increasedin short bursts to the ignition point of the electric arc.

The existence of the arc will be evidenced by the generation of theharmonics which will be detected by the measuring means. As soon as theignition point is reached at the time point "c", and this fact isdetected, the current magnitude at the moment will be measured, and itsmagnitude fed into the set-point program as a new standard. Then it isnecessary for the current immediately to be reduced so that the arc isextinguished, because cutting is not desired. The set-point program hasbeen given a suitable order or standard, i.e., the current level atwhich the arc ignites, and the next coagulation current will be relatedto it, and be less than the ignition value. The set-point programcontains data relating to the difference there should be between theactual current at ignition and the standard, and will therefore reducethe current by some predetermined amount.

During the searching for the ignition point at time points "c", it isimportant to take into account the fact that the arc will not startimmediately after the necessary current level enabling it has beenreached. It is, therefore, necessary to allow a little time (e.g., amilli-second) for the arc to start. This fact is related to the rate atwhich the current itself is to be increased. In a preferred form of thisinvention, enough time is allowed that the electric arc can occur and berecognized before an excessively large additional increase of current ismade. This is done in such a way that the current magnitude at the endof the time interval "b" and up to the ignition point "c" increasesgradually. If the increase is too sudden, then the current magnitudewould quickly rise above the ignition point, before the electric arc canoccur. It is best practice, if one is to find the exact ignition point,to allow the increase of current to occur in small steps and to permitits magnitude to hover at a nearly constant value at every step, andlengthen the duration of each step slightly more than the time thatwould be needed for ignition of the electric arc. Then the electric arcstarts at a current level respective to the exact ignition point.

It is of advantage to build the set-point program and the controlprocess utilizing digital principles, i.e., to increase the current stepby step, and to keep the time interval in every step equal to, or equalto a prescribed multiple of, a standard time interval. The set-pointprogrammer 9 will then include a clock which determines the intervalduration of the step and/or the interval of the standard time. Themagnitude of the steps will be preselected by the surgeon, and isrelated to the requirements of the operation procedure and the stepintervals. In bloodier environments requiring more coagulation, therewill be longer coagulation intervals than when tissue is being cut whichis not especially laden with blood, or wherein large vessels areexpected to be encountered.

The set-point program is produced by a logical circuit and determinesif, and in which predetermined time intervals (steps), the current willbe changed by an impulse device. Circuits for this purpose are wellknown, and require no detailed disclosure here. The control means 8 alsohas an electronic device that sets (in the preset time points "c") thelevel of the set-point program relative to the measured ignition levelof the electric arc.

There are cases in which the bleeding is expected to be very profuse,and in which the tissue will be cooled by the flowing blood. In thesecases one needs especially large amounts of heat to close the cut bloodvessels. In a favorable form of this invention, a large amount of heatcan be brought to the tissue for a very short time. This will beachieved by short impulses of high frequency current during thecoagulation interval to a point above the ignition point of the electricarc, but only for such a short duration that cutting itself does notoccur. This extreme heat acts only on the surface of the tissue and isrestricted to the immediate surroundings of the probe, so that theadverse effects on the albumen are at least localized, and anydisadvantage is offset by the promptness of coagulation.

The term "generator" has been utilized herein to describe a source ofcurrent at a predetermined frequency, usually a high frequency betweenabout 200 KHz-1.7 MHz, to produce currents that are acceptable to thehuman body. These are generally known surgical standards, and suchgenerators are widely known and require no further discussion here. Thefilters as described herein are conventional types which haveband-passes set to pass only the components of interest as describedherein. Such filters are completely conventional and require no detaileddiscussion here. The measuring mears may comprise conventional highfrequency ammeters or voltmeters, as indicated.

The reference setter 9 is a simple means to determine a predetermineddifference between the current at which ignition occurs and the currentwhich should be produced during coagulation. The control means is asimple sequential means operable in response to the input from leads 11and reference setter 9 to determine the output of the generator inaccordance with known techniques.

This invention thereby provides a means for limiting the volume of theelectric arc to the minimum extent necessary for the cutting of humantissue, and during coagulation to produce maximum heat without extendinginto the arc region by periodically referring the system to the point atwhich an arc is generated.

The means for determining the presence or absence of an arc may beoptical, such as an infrared or ultraviolet responsive sensor whoseproduction of an electrical signal would be detected, or, in thepreferred embodiment, an all-electrical circuit as already defined.

The term "measuring means" is sometimes used synonymously with"indicating means". Obviously, measuring means 16 and 18 by producing ameasurement, will also indicate the existence of an arc. In FIG. 2, theillustrated "indicating means" is simpler, and more generic, and maycomprise merely an optical-electrical means responsive to the arc. Assuch it is less sophisticated than the means shown in FIGS. 3 and 4,which also indirectly measure the volume of the arc. Of course,measuring means can be used also in FIG. 2, and FIGS. 3 and 4 show meansfor doing it. Of course, if measurements of the arc intensity are made,rather than of harmonics, then appropriate and straight forwardcircuitry will be supplied for that purpose.

This invention is not to be limited by the embodiments shown in thedrawings and described in the description, which are given by way ofexample and not limitation, but only in accordance with the scope of theappended claims.

We claim:
 1. A method of regulating the current applied to ahigh-frequency current tissue-coagulating device having a probe actingas one electrode, a second electrode, and a generator of high-frequencycurrent applying said current to said electrodes, said tissue having theproperty of steaming off when heated to high temperature, said methodcomprising regulating the current output of said generator so as togenerally maintain it below the current level at which an arc willignite at the probe by, at spaced-apart points in time raising thecurrent to a level at which an arc ignites, detecting said arc, andreducing the current to a lesser level at which the arc extinguishes,and supplying current at said lesser level for coagulating purposes. 2.A method according to claim 1 in which the current is alternately raisedto the ignition level and reduced by a predetermined amount therefrom.3. A method according to claim 2 in which the current output of saidgenerator is raised in steps, with a dwell period at each stepsufficient to permit the arc to ignite if it will ignite, before saidcurrent is again increased in case no arc ignites.
 4. Apparatus forcoagulating tissue utilizing current supplied by a generator,comprising:a generator for supplying current; a probe for making contactwith tissue to be coagulated by heat applied by the probe, the probefunctioning as an electrode; a second electrode; conductive lead meansconnecting said generator to the electrodes; indicating means responsiveto the existence of an electric arc between the probe and the tissue andproductive of an indication of the existence of an arc; and controlmeans to increase and to decrease the current supplied by the generator,said control means being so constructed and arranged as gradually toincrease said current to an ignition level at which an arc ignites, andresponsive to said indicating means so as to reduce said current outputfrom the generator after an arc has ignited to a lesser level at whichthe arc is extinguished, but at which coagulating heat is applied by theprobe.
 5. Apparatus according to claim 4 in which the control means isso constructed and arranged as to reduce the current level by apredetermined increment to said lesser level.
 6. Apparatus according toclaim 5 in which a reference setter is connected to said control meansto determine the size of said increment.
 7. Apparatus according to claim6 in which said reference setter includes means so constructed as atspaced-apart points in time during coagulating to raise the current to alevel at which the arc ignites, and then reduce the current by saidincrement.